The Ulumúri were the great horns of Ulmo, with which he made his music. Salmar, one of the Maiar, made the horns out of white shells.

Those who hear the music that Ulmo makes with the Ulumúri are caught up in it’s magic. The music is ever-present in their hearts and they are forever filled with a longing for the sea. Ulmo used the music of the Ulumúri to turn the Elves’ fear of the sea into a desire for it.
Encyclopedia entry originally written by Ringhilwen